I would like to know what to do if I eat a meal which is JUST Mezonot-like macaroni and cheese-or a few slices of "Mezonot pizza". Should I wash? What Brachot should I make? Is the amount important in grams or does it depend on whether or not you feel satisfied?

For pasta and similar Mezonot food that is not baked but cooked, the answer is simple; you will say Mezonot regardless to how much you eat. As for baked “Mezonot food” like Pizza, or as the Halacha calls them – “Pat Haba’a BeKisnin”; if you have them as a snack it will be Mezonot and if you make it your meal it will be treated just as bread. There is a Halachic dispute about what constitutes a “meal” and what a “snack”. To avoid entering a Halachic questionable situation, it is recommended not to eat more than about 200ml of that food unless if within a meal of bread. The details for this question are many and this is only a short and incomprehensive synopsis, for more detail you should look up the Shulchan Aruch OC 168 6-7 and the commentators related or look for a book of the laws of Brachot in English